A comment says
Actually, it's not the same question, because this question is about how the star "turns on" like a light, and exhibits confusion between that and the onset of fusion-- which is completely different. Fusion onset does not change the luminosity of a star, it merely allows the star to achieve equilibrium and a more gradual evolution rate. So this should be emphasized in the answer to this question-- regardless of the timescale for fusion to begin, the star is already bright.
There is now a vote to reopen and I'd thought about clicking "edit and reopen" but the question is by an unregistered user who has not been active since the moment the question was posted on May 12 2019.
In this particular case is it better to make a substantial edit and vote to reopen with the risk that a good answer will never be accepted, or to instead for someone (ideally the first reopen voter) to post a new question?